module top_module( 
    input [15:0] a, b, c, d, e, f, g, h, i,
    input [3:0] sel,
    output [15:0] out );
    
    always @(*) begin
        case(sel)
            4'b0000: out = a;
            4'b0001: out = b;
            4'b0010: out = c;
            4'b0011: out = d;
            4'b0100: out = e;
            4'b0101: out = f;
            4'b0110: out = g;
            4'b0111: out = h;
            4'b1000: out = i;
            default: out = 16'hffff;
        endcase
    end
endmodule